The present invention generally relates to a two-compartment type prefilled syringe in which the interior of a cartridge made of glass or plastic is divided into front and rear compartments by a plurality of rubber stoppers, and more particularly and to improvement of a bypass for communicating the front and rear compartments with each other which is formed by bulging a peripheral wall of the cartridge radially outwardly.
A two-compartment type prefilled syringe having such a construction is known from, for example, Japanese Patent Laid-Open Publication No. 62-5357 (1987) and Japanese Utility Model Publication No. 3-31302 (1991). In the known two-compartment type prefilled syringe disclosed in the former document, a first rubber stopper F disposed adjacent to a front sleeve L, a second rubber stopper D disposed adjacent to a finger grip N acting as an inlet for a plunger rod M and a third rubber stopper E disposed between the first and second rubber stoppers F and D are provided in a cartridge A made of glass or plastic as shown in FIG. 6. The interior of the cartridge A is hermetically divided into a front compartment C and a rear compartment B by the third rubber stopper E. The third rubber stopper E is constituted by a rear third rubber stopper E1 and a front third rubber stopper E2.
A bypass I for communicating the front and rear compartments C and B with each other is formed by radially outwardly bulging a portion of a peripheral wall of the cartridge A disposed between the first rubber stopper F and the third rubber stopper E.
In the known two-compartment type prefilled syringe having the construction shown in FIG. 6, the first rubber stopper F is displaced to a front end chamber Q2 through a front chamber Q1 at an initial stage of depression of the plunger rod M. By grooves R1 and R2 formed on an inner surface of a peripheral wall of the front end chamber Q2, the front chamber Q1 and the front end chamber Q2 are communicated with a bore P leading to an injection needle J. When the plunger rod M is further depressed, the second rubber stopper D is advanced, and thus the third rubber stopper E is pushed towards the front compartment C by the internal pressure of pharmaceutical liquid, such as dissolving agent H filled in the rear compartment B in liquid-tight condition.
At the moment the third rubber stopper E has been displaced into the bypass I, the rear compartment B and the front compartment C are communicated with each other by a gap between the bypass I and the third rubber stopper E, so that the pharmaceutical liquid, such as the dissolving agent H, of the rear compartment H flows into the front compartment C at a high velocity so as to suspend or dissolve dry medicament G. At an initial stage of communication between the rear compartment B and the front compartment C, the pharmaceutical liquid such as the dissolving agent H, which has passed through the bypass I, has high kinetic energy and thus, impinges like a squirt upon a rear face of the first rubber stopper F in the front end chamber Q2. As a result, the pharmaceutical liquid such as the dissolving agent H flows into the grooves R1 and R2 of the front end chamber Q2 while suspend the dry medicament G sufficiently or reaching the injection needle J from the bore P without dissolving the dry medicament G.
Meanwhile, the front third rubber stopper E2 is fitted into the cartridge A from the front chamber Q1 for the purpose of sealing the rear compartment B and the front compartment C in liquid-tight condition and preventing transfer of moisture to the dry medicament G of the front compartment C from the rear third rubber stopper E1 which has absorbed moisture by steam sterilization performed after pour and sealing of the pharmaceutical liquid such as the dissolving agent H.
On the other hand, in the conventional two-compartment type prefilled syringe disclosed in the latter document, a gasket S disposed adjacent to a finger grip Y confronting a plunger rod (not shown) is fitted into a peripheral wall of a cartridge K, while a first rubber stopper W is fitted into a front sleeve V as shown in FIG. 7. Furthermore, a third rubber stopper R3 is fitted inside the peripheral wall of the cartridge K so as to be disposed between the gasket S and the first rubber stopper W. The interior of the cartridge K is divided into a front compartment Q3 and a rear compartment Q4 by the third rubber stopper R3. The dry medicament G is filled in the front compartment Q3, while the dissolving liquid H is filled in the rear compartment Q4. A bypass T for communicating the front compartment Q3 and the rear compartment Q4 with each other is formed by radially outwardly bulging a portion of the peripheral wall of the cartridge K disposed between the first rubber stopper W and the third rubber stopper R3. A concave engageable portion P1 and a convex engageable portion P2 are, respectively, formed on a rear face of the third rubber stopper R3 and a front face of the second rubber stopper S so as to confront each other. When the rear face of the third rubber stopper R3 and the front face of the second rubber stopper S have been brought into contact with each other, the convex engageable portion P2 of the second rubber stopper S is brought into engagement with the concave engageable portion P1 of the third rubber stopper R3 so as to integrally couple the second and third rubber stoppers S and R3 with each other.
Prior to use of the conventional two-compartment type prefilled syringe of FIG. 7, a double-pointed needle (not shown) is mounted on the front sleeve V so as to pierce the first rubber stopper W. Subsequently, when the second rubber stopper S is advanced by the plunger rod screwed into a threaded portion of the second rubber stopper S, the internal pressure of the dissolving agent H of the rear compartment Q4 rises, so that the third rubber stopper R3 is advanced into the bypass T. At the moment the rear compartment Q4 and the front-compartment Q3 have been communicated with each other, the dissolving agent H, having high kinetic energy, is drawn into the front compartment Q3 like a squirt so as to reach the first rubber stopper W.
At the time the whole amount of the dissolving agent H in the rear compartment Q4 has displaced to the front compartment Q3, the second rubber stopper S is brought into contact with the third rubber stopper R3. Therefore, the convex engageable portion P2 of the second rubber stopper S is brought into engagement with the concave engageable portion P1 of the third rubber stopper R3 so as to couple the second and third rubber stoppers S and R3 with each other integrally.
In both of the prior art two-compartment type prefilled syringes of FIGS. 6 and 7, an operation for delivering the pharmaceutical liquid such as the dissolving agent in the rear compartment to the front compartment containing the dry medicament is performed in a state in which the injection needle is fitted into the syringe. Therefore, a drawback happen in that since only the pharmaceutical liquid leaks out of the injection needle prior to suspension or dissolution of the dry medicament due to the above mentioned squirt phenomenon of the pharmaceutical liquid such as the dissolving agent, the amount of the dissolving agent is less than that required for dissolving the dry medicament in the front compartment, thereby resulting in improper dissolution of the dry medicament.
In order to prevent the above mentioned squirt phenomenon of the pharmaceutical liquid, an operator has to adjust the depression of the plunger rod in a sophisticated manner, thus resulting in the disadvantage that it is extremely difficult to operate the syringe.
Furthermore, the only measure for preventing the squirt phenomenon in the constructions of the prior art two-compartment type prefilled syringes is to increase the volume of the front compartment to an unnecessary degree. Therefore, there has been a demand for a means for preventing the squirt phenomenon without incurring An increase in the volume of the front compartment.
In addition, it is not preferable that prior to injection, the dissolving agent adheres to an outer side of the injection needle and an inner side of a cap Z (FIG. 6) due to the squirt phenomenon.